275 lines
11 KiB
ReStructuredText
275 lines
11 KiB
ReStructuredText
System Add-ons Overview
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=======================
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System add-ons are a method for shipping extensions to Firefox that:
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* are hidden from the about:addons UI
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* cannot be user disabled
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* can be updated restartlessly based on criteria Mozilla sets
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Generally these are considered to be built-in features to Firefox, and the
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fact that they are extensions and can be updated restartlessly are implementation
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details as far as users are concerned.
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If you'd like to ship an add-on with Firefox or as an update (either to an existing
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feature or as a "hotfix" to patch critical problems in the wild) please contact the
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GoFaster team: https://mail.mozilla.org/listinfo/gofaster
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The add-ons themselves are either legacy Firefox add-ons or WebExtensions.
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They must be:
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* restartless
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* multi-process compatible
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Other than these restrictions there is nothing special or different about
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the extensions themselves.
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It is possible to override an installed system add-on by installing a different add-on
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with the same ID into a higher priority location.
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Available locations, starting from the highest priority include:
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1) temporary install (about:debugging)
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2) normal user install into profile (about:addons or AMO/TestPilot/etc.)
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3) system add-on updates
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4) built-in system add-ons
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This makes it possible for a developer or user to override a system add-on
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by installing an add-on with the same ID from AMO or TestPilot or as a temporary
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add-on.
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Default, built-in system add-ons
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--------------------------------
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The set of **default** system add-ons are checked into `mozilla-central` under
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`./browser/extensions`. These get placed into the `features` directory of the
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application directory at build time.
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System add-on updates
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---------------------
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System add-on **updates** are served via Mozilla's Automatic Update Service
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(AUS, aka `Balrog`_). These are installed into the users profile under the `features`
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directory.
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Updates must be specifically signed by Mozilla - the signature that addons.mozilla.org
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uses will not work for system add-ons.
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As noted above, these updates may override a built-in system add-on, or they may
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be a new install. Updates are always served as a set - if any add-on in the set
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fails to install or upgrade, then the whole set fails. This is to leave Firefox
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in a consistent state.
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System add-on updates are removed when the Firefox application version changes,
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to avoid compatibility problems - for instance a user downgrading to an earlier
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version of Firefox than the update supports will end up with a disabled update
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rather than falling back to the built-in version.
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Firefox System Add-on Update Protocol
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=====================================
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This section describes the protocol that Firefox uses when retrieving updates
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from AUS, and the expected behavior of Firefox based on the updater service's response.
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.. _Balrog: https://wiki.mozilla.org/Balrog
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Update Request
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--------------
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To determine what updates to install, Firefox makes an HTTP **GET** request to
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AUS once a day via a URL of the form::
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https://aus5.mozilla.org/update/3/SystemAddons/%VERSION%/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/update.xml
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The path segments surrounded by ``%`` symbols are variable fields that Firefox
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fills in with information about itself and the environment it's running in:
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``VERSION``
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Firefox version number
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``BUILD_ID``
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Build ID
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``BUILD_TARGET``
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Build target
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``LOCALE``
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Build locale
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``CHANNEL``
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Update channel
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``OS_VERSION``
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OS Version
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``DISTRIBUTION``
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Firefox Distribution
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``DISTRIBUTION_VERSION``
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Firefox Distribution version
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Update Response
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---------------
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AUS should respond with an XML document that looks something like this:
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.. code-block:: xml
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<?xml version="1.0"?>
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<updates>
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<addons>
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<addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/>
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<addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/>
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</addons>
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</updates>
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* The root element is ``<updates>``, used for all updater responses.
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* The only child of ``<updates>`` is ``<addons>``, which represents a list of
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system add-ons to update.
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* Within ``<addons>`` are several ``<addon>`` tags, each one corresponding to a
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system add-on to update.
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``<addon>`` tags **must** have the following attributes:
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``id``
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The extension ID
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``URL``
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URL to a signed XPI of the specified add-on version to download
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``hashFunction``
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Identifier of the hash function used to generate the hashValue attribute.
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``hashValue``
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Hash of the XPI file linked from the URL attribute, calculated using the function specified in the hashValue attribute.
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``size``
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Size (in bytes) of the XPI file linked from the URL attribute.
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``version``
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Version number of the add-on
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Update Behavior
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---------------
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After receiving the update response, Firefox modifies the **update** add-ons
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according to the following algorithm:
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1. If the ``<addons>`` tag is empty (``<addons></addons>``) in the response,
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**remove all system add-on updates**.
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2. If no add-ons were specified in the response (i.e. the ``<addons>`` tag
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is not present), do nothing and finish.
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3. If the **update** add-on set is equal to the set of add-ons specified in the
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update response, do nothing and finish.
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4. If the set of **default** add-ons is equal to the set of add-ons specified in
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the update response, remove all the **update** add-ons and finish.
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5. Download each add-on specified in the update response and store them in the
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"downloaded add-on set". A failed download **must** abort the entire system
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add-on update.
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6. Validate the downloaded add-ons. The following **must** be true for all
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downloaded add-ons, or the update process is aborted:
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a. The ID and version of the downloaded add-on must match the specified ID or
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version in the update response.
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b. The hash provided in the update response must match the downloaded add-on
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file.
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c. The downloaded add-on file size must match the size given in the update
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response.
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d. The add-on must be compatible with Firefox (i.e. it must not be for a
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different application, such as Thunderbird).
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e. The add-on must be packed (i.e. be an XPI file).
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f. The add-on must be restartless.
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g. The add-on must be signed by the system add-on root certificate.
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6. Once all downloaded add-ons are validated, install them into the profile
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directory as part of the **update** set.
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Notes on the update process:
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* Add-ons are considered "equal" if they have the same ID and version number.
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Examples
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--------
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The follow section describes common situations that we have or expect to run
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into and how the protocol described above handles them.
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For simplicity, unless otherwise specified, all examples assume that there are
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two system add-ons in existence: **FlyWeb** and **Pocket**.
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Basic
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~~~~~
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A user has Firefox 45, which shipped with FlyWeb 1.0 and Pocket 1.0. We want to
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update users to FlyWeb 2.0. AUS sends out the following update response:
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.. code-block:: xml
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<updates>
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<addons>
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<addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-2.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="2.0"/>
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<addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/>
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</addons>
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</updates>
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Firefox will download FlyWeb 2.0 and Pocket 1.0 and store them in the profile directory.
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Missing Add-on
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~~~~~~~~~~~~~~
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A user has Firefox 45, which shipped with FlyWeb 1.0 and Pocket 1.0. We want to
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update users to FlyWeb 2.0, but accidentally forget to specify Pocket in the
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update response. AUS sends out the following:
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.. code-block:: xml
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<updates>
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<addons>
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<addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-2.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="2.0"/>
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</addons>
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</updates>
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Firefox will download FlyWeb 2.0 and store it in the profile directory. Pocket
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1.0 from the **default** location will be used.
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Remove all system add-on updates
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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A response from AUS with an empty add-on set will *remove all system add-on
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updates*:
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.. code-block:: xml
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<updates>
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<addons></addons>
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</updates>
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Rollout
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~~~~~~~
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A user has Firefox 45, which shipped with FlyWeb 1.0 and Pocket 1.0. We want to
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rollout FlyWeb 2.0 at a 10% sample rate. 10% of the time, AUS sends out:
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.. code-block:: xml
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<updates>
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<addons>
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<addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-2.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="2.0"/>
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<addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/>
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</addons>
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</updates>
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With this response, Firefox will download Pocket 1.0 and FlyWeb 2.0 and install
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them into the profile directory.
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The other 90% of the time, AUS sends out an empty response:
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.. code-block:: xml
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<updates></updates>
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With the empty response, Firefox will not make any changes. This means users who
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haven’t seen the 10% update response will stay on FlyWeb 1.0, and users who have
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seen it will stay on FlyWeb 2.0.
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Once we’re happy with the rollout and want to switch to 100%, AUS will send the
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10% update response to 100% of users, upgrading everyone to FlyWeb 2.0.
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Rollback
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~~~~~~~~
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This example continues from the “Rollout” example. If, during the 10% rollout,
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we find a major issue with FlyWeb 2.0, we want to roll all users back to FlyWeb 1.0.
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AUS sends out the following:
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.. code-block:: xml
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<updates>
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<addons>
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<addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/>
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<addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/>
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</addons>
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</updates>
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For users who have updated, Firefox will download FlyWeb 1.0 and Pocket 1.0 and
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install them into the profile directory. For users that haven’t yet updated,
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Firefox will see that the **default** add-on set matches the set in the update
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ping and clear the **update** add-on set.
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